don't use preload_associations

it's a shim of the rails 2 variety, and breaks in rails 4 in the
common case because the options became a scope

Change-Id: I712a8fed35ee0a9747a13c1495f7d51b8dac6823
Reviewed-on: https://gerrit.instructure.com/41716
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Nick Cloward <ncloward@instructure.com>
Product-Review: Cody Cutrer <cody@instructure.com>
QA-Review: Cody Cutrer <cody@instructure.com>